How to prevent damping off

BBC Gardeners' World Magazine

Published: Thursday, 25 April 2019 at 2:19 pm

Sowing seeds? Discover six ways to avoid damping off and keep your seedlings healthy.

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When you've sown your seeds in spring, it can be very disappointing if they germinate poorly, or fail to thrive.

Seeds and seedlings are prone to a fungal infection called 'damping off'. The very visible collapse of the seedlings is often accompanied by a mass of tiny fungal threads. The fungi develop from microscopic spores that can be both air and waterborne.

Good hygiene is very important, so be sure to use clean equipment and fresh compost. Damping off is encouraged by damp, overcrowded conditions and poor ventilation, so you need to provide the optimum conditions for your seeds.

Here are six ways to avoid damping off and to keep your seedlings healthy.

Wash all pots and trays

Microscopic fungi can survied on previously used pots and seedtrays. Washing equipment will help to remove the majority of the spores and decrease the risk of infection. Soak your pots and trays overnight in buckets or tub trugs of water containing a solution of horticultural disinfectant to moisten any dried-on compost. Once loosened, it will easily scrub off before your containers are rinsed with clean water. Don't forget to clean propagator lids, too.

Scrubbing soaked plant pots clean

Use fresh compost

Fungal spores are also able to survive in old compost, so for your best chance of success, use a new bag of good-quality sowing compost.

Adding compost to a large planter

Add perlite to compost

Improve the drainage and aeration of compost at the surface by adding perlite or coarse grit in equal parts by volume. This will reduce moisture and humidity levels, which encourage the germination of fungi spores that swamp seeds and seedlings.

Adding white perlite to compost

Sow in cellular trays

Create individual pockets of compost, using pots or cellular trays, to sow two or three seeds into. This will contain any fungal outbreaks of damping-off disease and help to limit its spread among seedlings, so improving their percentage survival rates.

Sowing seeds into cellular trays

Water from below

Stand sown seedtrays or pots in a bowl or bucket filled with 2.5cm of water. Leave in place for about 10 minutes. This will allow water to soak up from the bottom to moisten the compost, rather than soaking the surface where fungal spores tend to thrive.

Placing a planted seed tray into a shallow trug of water

Open propagator vents

Make sure that you ventilate propagators to prevent excess humidity building up, encouraging fungal growth. Open vents during the day and close at night to retain warmth. Use a cloth to wipe out the condensation from the inside of the propagator cover.

Propagators with their vents open

Avoid using rainwater

Don't use rainwater to water your seedlings - it could contain fungal spores.

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